This invention relates to a magnetic resonance imaging (abbreviated hereinafter as an MRI) apparatus utilizing the phenomenon of magnetic resonance, and more particularly to a method in which a human body is imaged by the MRI apparatus to determine a selected region of the human body on the image so as to determine the median line of the selected region of the human body.
In an MRI apparatus, a magnetic field is applied to a human body to induce the phenomenon of magnetic resonance of protons in a selected region of the human body, and the resultant magnetic resonance signal is detected and measured to display a tomographic image of the selected region of the human body. When the mode of application of the magnetic field (referred to hereinafter as a sequence) is changed in this MRI apparatus, the corresponding resonance signal can be obtained, so that, for example, the blood vessel only can be selectively imaged.
When a desired tomographic image of a selected region of a human body is to be obtained by this MRI apparatus, a plurality of tomographic images are first taken, and, after determining the desired slice direction on the basis of the anatomical information derived from these tomographic images, the most suitable sequence is selected so as to take the desired tomographic image. Thus, it is required to take a plurality of tomographic images for the purpose of positioning and also to determine the slice direction in order to obtain the desired tomographic image.
In our earlier invention described in patent application Ser. No. 07/870295 filed in the United States on Apr. 17, 1992, a method for automatically determining a sequence used in a usual diagnosis (a routine diagnosis) and a slice direction is registered beforehand, so that the desired tomographic image can be obtained by a single manipulation. In regard to the positioning, the patent application describes that characteristic regions of a human body are detected for the purpose of positioning and describes also a method for positioning, for example, the OM line of the head or the sagittal section of a transverse image of the neck.
Besides the method described above, a method in which the median line of a human body commonly used as an index in, for example, image measurement by the Hough transform is reported in IEEE TRANSACTIONS ON MEDICAL IMAGING, VOL. 10, NO. 1, MARCH 1991.
The above report refers to a method for detecting the median line in a transverse image and a coronal image of the head of a human body. According to the reported method, the head image is subjected to filtering (the Sobel operation) so as to be converted into an edge emphasized head image, and its binary image is subjected to the Hough transform so as to provide the desired median line.
When a different sequence is used in the MRI apparatus imaging a human body, a correspondingly different resonance signal is generated from the human body. This feature is widely utilized in the research and development of various sequences. That is, not only detection of a proton density image but also implementation of an angio sequence for selective measurement of a blood vessel and an ultra-high speed sequence for imaging with a very short imaging period of time are widely attempted.
Under such a background, MRI apparatuses have been improved from year to year to be able to operate with a higher performance, and the applicable range has also been progressively widened. However, with the improvement in the performance of the MRI apparatuses, they have inevitably the problem of requiring a complicated manipulation.
When a tomographic image of a desired region of a human body is required by a doctor for the purpose of diagnosis, a plurality of tomographic images are first taken, and, on the basis of the anatomical information derived from those tomographic images, the doctor determines the desired slice direction so as to obtain the desired tomographic image. Among the information used by the doctor during the process of imaging, the median line [which is the intersection line between the surface of the desired region of the human body and a perpendicular plane (a superior sagittal section) including a sagittal direction of a horizontal line penetrating the human body, that is, a plane (a median section) dividing the human body into its right and left halves] is very important information for accurately obtaining the tomographic image of the desired region of the human body.
The Hough transform described in the above paper as a method of determining the median line uses the sine and cosine functions for the determination. Therefore, the disclosed method used for the determination of the median line has the problem that an increase in the number of factors to be processed results in a corresponding increase in the period of time required for the processing.